1. Field of the Invention
This invention relates to transporting fluids in a conduit containing water and hydrocarbon wherein the fluid flow friction loss is reduced by incorporating within the water phase of the fluid a viscoelastic polymer obtained by radiation-induced polymerization.
2. Description of the Prior Art
It is generally known that high molecular weight polymers are useful as drag-reduction agents in the transportation of fluids during turbulent flow. Drag reduction as used herein includes reducing the fluid flow friction loss in the transmission of fluids through conduits. Of course, reducing the drag also reduces pumping requirements and hence the cost of transporting fluids through conduits or pipelines. This phenomenon has been reported in "Turbulence Studies of Steady and Pulsed Flow of Drag Reducing Solutions", Thomas, Greene, Nokes, and Chu, The University of Akron, and "Drag Reduction in Non-Aqueous Liquids", Ramakrishnan and Rodriquez, Cornell University, both of these papers given at the 72nd National Meeting of the American Institute of Chemical Engineers at St. Louis, Missouri, May 21-24, 1972. These papers generally conclude that the drag reduction decreases as the concentration of the polymer increases up to an "optimum concentration". Also, the papers conclude that the optimum concentration decreases as the molecular weight of the polymer increases.
Patents representative of this art include U.S. Pat. No. 3,493,000 to Canevari et al which teaches that reduction in friction losses are obtained with addition of polydimethylsiloxane, cis-polyisoprene, cis-polybutadiene, and ethylene dipropylene copolymer; these polymers having average molecular weights in the range of 3-30,000,000 and preferably 7-20,000,000.
U.S. Pat. No. 3,472,769 to Lummus teaches synergistic action between a thickening agent and a friction-reducing agent to improve hydraulic friction characteristics of drilling fluids. The thickening agent can be methylcellulose, guar gum, completely hydrolyzed polyacrylamide, copolymer of methyl vinyl ether and maleic anhydride and a copolymer of vinyl acetate and maleic anhydride. The friction-reducing agent can be a copolymer of acrylic acid and acrylamide, a dextran-type polysaccharide, etc.
U.S. Pat. No. 3,542,044 to Hansen et al reduces energy loss during flow of oil through a pipeline by admixing with the oil an aqueous polyacrylamide solution preferably containing a dispersing agent. The polyacrylamide should have a molecular weight of at least 3,000,000 and should have about 5-40% of the original amide groups hydrolyzed to carboxylic groups. Such polymers are known as partially hydrolyzed, high molecular weight polymers. The patent mentions that polyisobutylene is useful as an oil-based friction reducer but that such is not readily dispersible and is sensitive to shear and high temperature; and, as a result, upon dissolution by heating and stirring, the effectiveness of the polyisobutylene is reduced.
U.S. Pat. No. 3,681,215 to Peterson teaches preparing water-soluble polymers containing at least 50% of acrylamide by dissolving vinyl and acrylamide monomers and an organic acrylic azo compound (as catalyst) in liquid ammonia (the ammonia can contain up to 25% water but is preferably anhydrous) and thereafter irradiating the mixture at a temperature less than 50.degree. C. The liquid ammonia functions as a reaction solvent for acrylamide and the other vinyl monomers. The irradiation is only used to activate the organic acrylic azo compound which in turn catalyzes the polymerization process.
Examples of patents which teach high molecular weight polyacrylamides include U.S. Pat. No. 2,842,492 to Engelhardt et al; U.S. Pat. No. 3,002,960 to Kolodny; U.S. Pat. No. 3,020,953 to Zerweck et al; U.S. Pat. No. 3,025,237 and 3,070,158 to Roper; Canadian Pat. No. 683,476 to Siegel et al; U.S. Pat. No. 2,827,964 to Sandiford et al; and U.S. Pat. No. 3,037,529 to McKennon.
The most effective drag-reducing polymers are those with a linear, flexible structure which achieve a spherically symmetric distribution of mass elements along the center of mass (random coil) when placed in solution. Also, drag reduction with very dilute polymer solutions is observed to increase with molecular weight of the polymer, concentration of the polymer, and solvent wall shear stresses.